Various conductive pastes comprising copper powders and binder resins are known. Examples of such conductive pastes include electroconductive pastes used as circuits and electroconductive adhesives, and thermally conductive pastes.
But, copper oxidizes easily, and when an electroconductive paste in which a copper powder is used as a filler is applied, and heated and cured in the air, an oxide film of copper is easily produced by reaction with oxygen. A problem is that because of the influence of the oxide film, the electrical resistance increases.
On the other hand, conventionally, a variety of composite materials obtained by mixing, in addition to a metal powder such as a copper powder and a binder resin, carbon fibers exhibiting high electroconductivity are also proposed.
However, in the materials comprising carbon fibers, the carbon fibers tend to aggregate when the carbon fibers are dispersed and in coating.
The following Patent Literature 1 discloses a method of placing a metal catalyst on a metal surface and producing carbon nanotubes with the metal catalyst. The carbon nanotubes are connected to the metal surface, and therefore the aggregation of the carbon nanotubes is less likely to occur.